Hybrid electric vehicles can achieve significant improvements in fuel economy and emissions compared to conventional engine powered vehicles without compromising vehicle performance (e.g. vehicle acceleration). The hybridization is accomplished by integrating an electric drive system into a conventional vehicle powertrain. Hybridization is the enabler to 1) downsize the engine for better overall engine operating efficiency; 2) eliminate relatively inefficient engine operating conditions by using electric drive and engine start/stop features; and 3) capture vehicle kinetic energy by using regenerative braking and storing captured energy in the battery.
A hybrid vehicle powertrain typically has two power sources; i.e., an internal combustion engine and a battery-motor system that can provide power to propel the vehicle to meet a driver demand for power. Coordination of control of multiple power sources would maximize benefits of hybridization and would satisfy driver power demand while ensuring compliance with constraints or limits for powertrain subsystems and components. This would avoid damage or a shortened expected life of the subsystems and components.